This application accompanies a proposal entitled "Randomized Trial of 11-14 Week Amniocentesis and TA CVS" submitted by Dr. Laird Jackson leading a group of twelve clinical centers. Together the proposals request funding for a multi-center randomized clinical trial of amniocentesis and transabdominal chorionic villus sampling (TA CVS) at 77-14 days gestation. This application proposes The George Washington University/Biostatistics Center as the Data Coordinating Center (DCC) for the study. The purpose of the study is to compare the two prenatal diagnosis techniques with regard to safety, measured primarily by a combined endpoint of fetal loss or preterm delivery before 196 days gestation and also by total fetal loss, amniotic fluid, gestational age at delivery, perinatal morbidity, neonatal morbidity and congenital abnormalities, including limb reduction effects. Success in obtaining a diagnosis from the two procedures will be compared. An ancillary study will evaluate the feasibility and accuracy of fluorescence in situ hybridization (FISH) as a rapid diagnostic method for certain cytogenetic abnormalities. A total of 6400 healthy pregnant women at 77 to 104 days gestation, whose only indication for prenatal diagnosis is advanced maternal age of at least 34 years at enrollment or trisomy in a previous pregnancy will be randomized to receive either TA CVS or amniocentesis following a baseline ultrasound. Five thousand eligible women who refuse randomization or for whom a procedure cannot be scheduled by 104 days will also be followed, one thousand of whom will have a standard amniocentesis procedure. The DCC will assist the group in implementing the study by: (1) setting up a randomization procedure;' (2) training study personnel; (3) setting up a computerized data processing an editing system; (4) monitoring recruitment, protocol adherence and data quality; (5) preparing interim analyses of the results for a Safety monitoring Committee; (6) conducting final analyses and preparing the publication of results; and (7) documenting the final data base.